1. Technical Field
The present invention generally relates to a material handling system and more particularly, to a roller bed conveyor, such as an accumulator conveyor system, wherein limited and controlled slip between the roller surface and drive system is desired.
2. Related Art
Roller conveyors are commonly found in a variety of manufacturing, distribution and other warehouse facilities. Most roller conveyor systems include a variety of straight and curved segments configured to allow products, individually or packaged together, to travel through a facility, past various operations and to various destinations. Roller conveyor systems may also be an accumulation conveyor system, configured to allow live storage of products or accumulation of loads on the conveyor system. Accumulator conveyors are configured to stop and start various segments or portions of segments as needed and to allow packages or loads to selectively accumulate or be conveyed to a destination. Many accumulator conveyors are used in warehouse or distribution centers where accumulator conveyor segments feed onto a main line, with each accumulator conveyor segment feeding the main line with a single product. A control system may control the timing of each accumulator conveyor segment feeding the main line so that all products or packages going to a particular destination are clearly delineated and ready for shipment as a group. Therefore, as an order for a variety of products is placed in the system and then prepared for shipment, each of the accumulator conveyors feeds the desired amount of product onto the main line and the main conveyor line conveys the products or loads to a shipping point where as a group they are packaged together, such as on a pallet or in a box, and shipped out together. An example of an accumulator system would be a system in a beverage distribution facility with a multitude of individual beverage products, such as cases of cans, bottles, or even totes of two liters, which feed onto a main line where they are packaged together to a final destination point. As the order is processed, particular beverages from individual conveyor segments are fed onto the main line and timed such that as the order passes down the main line, additional products for that order are fed onto the main line, creating a grouping of loads on the main line for a single destination.
With heavier loads such as beverages, which have a high weight in a small space, traditional accumulator lines that use a single start and stop mechanism are expensive, difficult to properly operate and have problematic operational considerations due to the dense packing of heavy loads on most accumulator conveyor systems. More specifically, a long row of heavy loads, such as beverages, when tightly packed that must be stopped and started over and over, sometimes moving precisely only a single load forward or onto an intersecting or main conveyor segment, requires substantial force to start and stop and the start and stop mechanisms must be robustly built to take a lifetime of stops and starts without breakdown, which results in expensive mechanisms. As such, it would be desirable to space the loads sufficiently apart; however, in many accumulator conveyor systems, the loads are packed as tightly as possible to maximize live storage on the conveyor system, which creates operational difficulties in efficiently and consistently stopping and starting in a reliable manner. Therefore, when the conveyor starts, for densely packed loads, the motor must drive a large segment such as a 20 foot segment of a roller bed feeding power to each roller and moving the 20 foot segment of product or loads forward in unison. This can be extremely hard on the motor as well as the drive connection between the rollers and motor, particularly when the loads are densely packed on the system without gaps, and are a heavy dense material, such as beverages, laundry detergent, and metal hardware.
In addition, accumulator conveyor systems are generally price-sensitive and the addition of cost to any one area generally must be offset by a reduction in price on other parts of the conveyor system. Therefore, it is difficult to use more expensive rollers or drive systems, to offset the extreme wear caused by the heavy densely packed loads. While some manufacturers have proposed expensive clutches attached to the motor, in addition to problems with price sensitivity, these clutches have particular problems with starting and stopping the motor, such as for heavier loads excessive wear and tear which may cause shortened life expectancy, or may require more robust clutch systems that are substantially more expensive. In addition, the motor, even if a clutch is used to protect the drive system between the clutch and each roller, may experience wear. While some manufacturers have attempted to clutch individual rollers for larger pallet conveyor systems, these clutched rollers are extremely large and to date have been too expensive and too large to be practical in most settings other than pallet conveyors. As such, not only has the cost, but also their size prevented them from being used in most package and beverage conveyor systems. In addition, for most roller conveyors that are not pallet conveyors, the slip must be a very light pressure, no more than needed to drive forward the expected load on each roller. For example, a load that is less than thirty pounds may need only 0.5-5 lbs. and for beverages 3-5 lbs. of total force to start the load in motion and then drive the load forward. When the load is spread across multiple rollers, the maximum force applied by each roller may be very small, typically dividing the total force by the number of supporting rollers. For example, if the load spans two or three rollers, a load requiring 3-5 lbs. of force, each roller should have no more than about 1-2 lbs of torque, typically less, of forward pressure applied by each roller to the load. Any higher forward pressure and the system will not allow for controlled slip situations, and may damage the system or loads. More specifically, if there is a fifty foot accumulator conveyor, which many accumulator conveyor systems include even longer runs, and each roller applies a 1-2 pound pressure and there are one hundred total rollers, the pressure applied in a no gap between loads configuration may easily be 100-200 pounds of force against the mechanism, such as a gate, that controls releasing the next load from the run to another segment. To date no system efficiently and in a reliable manner applies a light enough load for under fifty pound packages or loads on the system when the clutch system is coupled to or within each roller. More specifically, a light load applied by each roller has been difficult to consistently achieve with each roller applying less than 5 lbs. on average, preferably less than 2 lbs., and in many instances well under a pound of force, before slip occurs within the roller and not between the roller and the load. In addition, current clutches attached to each roller are not cost effective when compared to single clutch systems, which include the above identified problems.